Question SSDs are slow (800MB/s) on ASRock B560M Pro4

[VcSaJen]

Motherboard: ASRock B560M Pro4
CPU: Core i5 10400F (LGA-1200/Comet Lake)
GPU is on PCIE1 slot
PCIe-to-M.3 NVMe adapter: Ugreen CM302 on PCIE3 slot
(M2_1 slot is disabled because CPU is Comet Lake)
SSDs:
- Kingston SKC2500M8/1000G via adapter
- Silicon Power US70 (2 TB) [SP02KGBP44US7005] on M2_2 slot

For a year I had Kingston SKC2500M8 on M2_2 slot. I think speed was fine for PCIe 3.0 x4. So now I bought a second SSD and an adapter, moved Kingston to adapter, and installed Silicon Power to M2_2 slot. I booted up, checked them in CrystalDiskMark, and the speed is awful, barely 800MB/s:

CrystalDiskInfo lists Transfer Mode of Kingston as "PCIe 3.0 x4 | PCIe 3.0 x4" and Silicon Power as "PCIe 3.0 x4 | PCIe 4.0 x4".
What is happening here? Why both of them become so slow? I read motherboard manual, there are no "gotchas" here, PCIE3 slot should unconditionally be PCIe 3.0 x4, and M2_2 should give PCIe 3.0 x4 speed when in NVMe mode.
How do I fix it?
Edit:
Here's what HWiNFO64 shows:

Spoiler: HWiNFO64

 

[rocktalkrock]

Have you looked at the drives using the Silicon Power ToolBox or Kingston SSD Manager software?

 

[VcSaJen]

Tried to disconnect one SSD to test if it's fast with just one SSD. Nope, just Kingston on adapter: slow, just Kingston on M2_2: slow, just SP on M2_2: slow.

Have you looked at the drives using the Silicon Power ToolBox or Kingston SSD Manager software?

Yes, but there's nothing useful there. No errors or anything.
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Edit: After reseating them both one last time, now they're both fast (3.4GB/s read, 2.7GB/s write). I have no idea why they were slow. I have no idea why they're now fast. I guess problem is solved... somehow.
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Edit 2: Now it's slow again... but after reboot it's fast again. Any way to determine the cause of this randomness?